The present invention generally relates to drill bits for boring subterranean and sub sea formations. More particularly, the present invention relates to a lubricating nutating single cone drill bit having an axis of rotation skewed relative to the central axis of the bit body in the borehole providing low torque and allowing high compressive loading on the bit assembly.
A number of single cone drill bits have been proposed through the years to drill bore holes for mining, oil and gas exploration, and utility construction. It has been previously recognized that a single cone bit would offer superior design characteristics, such as bearing size permitting greater longitudinal compressive loading on the drill bit. Previous single cone drill bits however provided substantial scraping of the cutter elements causing abnormal wear and torque on the drill string assembly.
Each of the prior single cone drill bits were subject to excessive wearing of the cutting elements because at least during some portion of the rotation, the cutter elements were dragged by the circular motion of the bit on the journal across the formation face rather than moved in compressive engagement with the surface. These cutter elements are designed to have long use lives if used in compression, but have a tendency to break if subjected to side shear or scraping. A nutating single cone drill bit, for example the one disclosed in U.S. Pat. No. 6,892,828, incorporated by reference herein, can offer the advantage of long wearing cutter elements. Typically, traditional tri-cone bits must be repeatedly tripped out of the borehole due to excessively worn cutter elements. Since a nutating single cone drill bit allows for longer service life, the extended periods of down-hole use can be limited by the amount of available lubrication sufficient to maintain the bearings of the nutating single cone bit. Without sufficient lubrication, the bearing can fail prior to the cutter elements of the bit wearing, limiting the usefulness of the nutating single cone drill bit.